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    Subject[Linux-kernel-mentees] [PATCH v1] usbhid: Fix slab-out-of-bounds write in hiddev_ioctl_usage()
    Date
    `uref->usage_index` is not always being properly checked, causing
    hiddev_ioctl_usage() to go out of bounds under some cases. Fix it.

    This patch fixes the following syzbot bug:

    https://syzkaller.appspot.com/bug?id=f2aebe90b8c56806b050a20b36f51ed6acabe802

    Reported-by: syzbot+34ee1b45d88571c2fa8b@syzkaller.appspotmail.com
    Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
    ---
    This patch fixes the bug, but in an ugly way. Checks on `uref` are already
    being done in this code:

    if (cmd == HIDIOCGCOLLECTIONINDEX) {
    if (uref->usage_index >= field->maxusage)
    goto inval;
    uref->usage_index =
    array_index_nospec(uref->usage_index,
    field->maxusage);
    } else if (uref->usage_index >= field->report_count)
    goto inval;

    However it did not catch this bug since it's in an `else` bracket. Should
    we move the above code out of the bracket? Would like to hear your opinion.
    Thank you!

    drivers/hid/usbhid/hiddev.c | 2 ++
    1 file changed, 2 insertions(+)

    diff --git a/drivers/hid/usbhid/hiddev.c b/drivers/hid/usbhid/hiddev.c
    index 4140dea693e9..c63d07caacef 100644
    --- a/drivers/hid/usbhid/hiddev.c
    +++ b/drivers/hid/usbhid/hiddev.c
    @@ -525,6 +525,8 @@ static noinline int hiddev_ioctl_usage(struct hiddev *hiddev, unsigned int cmd,
    goto goodreturn;

    case HIDIOCSUSAGE:
    + if (uref->usage_index >= field->report_count)
    + goto inval;
    field->value[uref->usage_index] = uref->value;
    goto goodreturn;

    --
    2.25.1
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